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This is part of Fig. 9 from the 2013 GENOPT paper2. Shown here are results from the specific case called “twoskirt”: Two axisymmetric vibration modes from GENOPT/BIGBOSOR4 for the optimized propellant tank with two skirts attached to the tank at the aft and forward cylinder-dome junctions. (A) Rolling of the propellant tank with in-plane shearing of the laminated composite skirts; (B) Very, very small axial motion of the propellant tank with local axisymmetric bending of the skirts near the tank/skirt junctions. Compare the GENOPT/BIGBOSOR4 predictions in this slide with predictions from STAGS shown in Figs. 10b. Note that the vibration mode characterized by mostly “rigid body” axial displacement of the tank, analogous to that displayed in Fig. 4(B) for the "oneskirt" configuration, was never found. It has a modal vibration frequency that is higher than the 10th eigenvalue for n = 0 circumferential waves, since all of these 10 modes [only the first of which is displayed here in (B)] involve deformation of the domes with little overall extension/compression/shearing of the skirts.
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